Transducer cartridge for precision gages



Nov. 30, 1965 R. E. RoEGER 3,221,281

TRANSDUCER CARTRIDGE FOR PRECISION GAGES Filed Nov. 15, 1962 ATTORNEY.

United States Patent O 3,221,281 TRANSDUCER CARTRIDGE FOR PRECISION GAGES Richard E. Roeger, Cleveland, Ohio, assignor, by mesne assignments, to The Bendix Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 13, 1962, Ser. No. 236,836 2 Claims. (Cl. 336-30) The present invention relates generally to transducers for precision gages and more particularly to mechanical input inductance variation type transducers.

The transducer of the present invention is adapted for used in gages, comparators and the like, where very precise measurements, e.g., to millionths of an inch, are involved.

It is an object of the present invention to provide a transducer for precision gages which has a highly sensitive and linear output over a relatively wide range of input displacements.

It is a further object of the invention to provide a transducer having a construction which may be easily manufactured to provide uniform characteristics so as to permit interchangeability of transducers in a gage or gaging system.

It is another object of the invention to provide a transducer which is small in size, reliable in operation with a high degree of sensitivity and repeatability and having a rugged construction so as to maintain its accuracy for a relatively long period of time and throughout a relatively wide range of operating and environmental conditions.

These and other objects and advantages of the present invention will become readily apparent following detailed description taken in connection with the appended drawings in which:

FIGURE 1 is a longitudinal sectional view of a trans ducer cartridge embodying the present invention;

FIGURE 2 is a sectional View taken along line 2-2 of FIGURE 1;

FIGURE 3 is a schematic view showing the magnetic circuit of FIGURE l.

Referring now to the drawings, and more particularly to FIGURE l, numeral designates a transducer having a magnetic main body 12, and a nonmagnetic end cap 14 through which an insulated electrical conduit 16 passes into the interior of body 12. A magnetic sleeve 18 is mounted in body 12 and receives a nonmagnetic cylindrical coil assembly 20 formed with a plurality of spool sections 22, 24 and 26 on which are respectively wound coils 28, and 32. A pair of magnetic annular members 34, recessed as at 36 are secured to the opposite ends of sleeve 18. Each of the annular members 34 threadably receive a magnetic cylindrical pick-up pin 38. Armature 44 is reciprocably mounted within the pick-up pins 38 and coil assembly 20 and is provided with a central magnetic portion 46 and non-magnetic end portions 48 and 50 which are mounted on nonmagnetic bolt 51. A nonmagnetic at spring 52 is peripherally clamped between an annular member 34 and a nonmagnetic plug 54 which is secured in main body 12. Spring 52 is centrally clamped to the end portion of armature 44 by a nonmagnetic nut 56. The second nonmagnetic at spring 58 is peripherally clamped between the other of the annular members 34 and a shoulder 60 formed in main body 12. Spring 58 is centrally clamped to end portion 48 of armature 44 by a nonmagnetic nut member 62 to which is secured a nonmagnetic tip member 64. The main body 12 is provided with a bore 66 through which the tip member 64 extends. An adjustable nonmagnetic screw 68 is mounted in body 12 and adapted to engage nut member 62 so as to limit the travel of armature 44 in one direction.

ICC

Plug 54 is provided with a cylindrical recess 70 to receive the armature nut 56. A light compression spring 72 is disposed to react between the end of recess 70 and the nut 56 to urge the armature 44 to the left as viewed in FIGURE 1.

The at springs 52 and 58 are identical in construction and as best seen in FIGURE 2, spring 52 is a flat resilient disc having three notches 74 formed equidistantly on the periphery thereof. The disc is also provided with four groups of arcuate slots 76, 78, and 81 disposed in concentric rings with each group having three slots 76abc, 78abc, 80abc and 81abc. The slots are disposed so that the center of the slots of one group are located intermediate the ends of adjacent slots in the group formed on the next larger diameter ring. When the armature 44 is moved by the application of force on tip 64, the springs 52 and 58 will flex along tortuous paths from the preiphery around the arcuate slots to the center of the disc.

Springs 52 and 58 permit the armature 44 to be moved axially but restrain the armature from radial movement. Springs 52 and 58 are designed to have a substantially constant spring rate throughout the design range of axial displacement of armature 44. The use of springs 52 and 58 permits the transducer to be constructed with a relatively small diameter. In one practical design embodying the present invention, the transducer has an outside diameter of 3A; of an inch.

Referring now to FIGURE 3, armature portion 46 is shown in the neutral or null position wherein the differential voltage of secondary coils 28 and 32 is zero. The lines of magnetic flux are shown pictorially. The ux from the primary coil 30 which links or couples the sec ondary coils has a principal path or magnetic circuit through armature portion 46, air gap 82, one of the pickup pins 38, sleeve 18, the other of the pick-up pins 38 and air gap 84 to the armature. As shown a small amount of the linking ux passes from the armature across an air space and through the inner ends of secondary coils 28 and 32 to sleeve 18.

In a preferred embodiment the pick-up pins 38 extend axially inwardly through substantially the full axial length of the secondary coils whereby all of the linking flux passing through the secondary coils passes through the pickup pins. The length of pick-up pins 38 is not critical but improved results are obtained if the pins extend at least halfway through the secondary coils. If the pick-up pins are removed, the sensitivity of the transducer is reduced markedly.

As the armature portion 46 is moved from its null position, as by way of example to the right as viewed in FIGURE 3, air gap 82 is decreased and gap 84 is increased thereby respectively decreasing the reluctance in the magnetic circuit linking coil 32 and increasing the reluctance in the magnetic circuit linking coil 28. The changes in reluctance changes the number of lines of ux linking the coils but does not substantially change the ilux path so that all of the turns of the secondary coils continued to be coupled by whatever flux is passing through the pick-up pins. The above described changes in reluctance will cause the voltage induced in coil 32 to increase and the voltage induced in coil 28 to decrease. The secondary coils are connected in such a manner that the differential voltage between the coils appears in the output leads 86 and 88. The output leads are adapted to be connected to suitable amplifying and indicating apparatus not shown.

The primary coil 30 is excited from a suitable source 90, which in a preferred embodiment is a 60 cycle source 0 although it is to be understood that other frequencies may be used.

Patented Nov. 30, 1965 The pick-up pins 38 may be readily adjusted to regulate the secondary outputs to provide the desired sensitivity for a given displacement of the armature from the null position. The pins 38 may, however, be iixed and desirable sensitivity obtained by adjusting a small variable resistor 92 in lead 88; or the resistor may be used in conjunction with adjustable pins 38. The above adjustments readily correct for manufacturing tolerances and imperfections in the secondary coils such as variations in cross sectional area over the length of the coils. Once the initial balance has been obtained at the null point the linearity of the transducer output is not substantially affected by such coil imperfections since With the use of the pick-up pin of the present invention the number of turns linked in the secondary coils is substantially constant throughout the range of axial movement of the armature.

Although only one embodiment has been shown and described, it will be readily apparent to those skilled in the art that various changes and modifications may be made Without departing from the spirit of the invention.

I claim:

1. In a transducer for a gage, comparator or the like comprising: magnetic housing means, a pair of coaxially spaced secondary coils in said housing means, a primary coil in said housing means disposed intermediate said secondary coils and coaxial therewith, a magnetic pickup pin for each of said secondary coils, said pickup pins being mounted in said housing to extend axially into said secondary coils at least half the axial length of said secondary coils, an armature mounted in said housing for reciprocation along the axis of said coils, said armature having non magnetic end portions disposed at least partly Within said pickup pins and a magnetic central portion disposed intermediate said pickup pins, whereby reciprocation of said armature varies the reluctance in the magnetic circuit between the magnetic central portion of said armature and said pickup pins, said pickup pinsv together With a portion of said housing means forming part of the magnetic circuit for the flux from said primary coil whereby the secondary coils are linked through substantially their entire axial length by said iluX substantially independently of the position of said armature, and annular at leaf springs secured to the non magnetic end portions of said armature and said housing means for resiliently supporting said armature for axial movement and constraining said armature against radial movement.

2. In a transducer for a gage, comparator or the like comprising: magnetic housing means, a pair of coaxially spaced secondary coils in said housing means, a primary coil in said housing means disposed intermediate said secondary coils and coaxial therewith, a magnetic pickup pin for each of said secondray coils, said pickup pins being mounted in said housing to extend axially into said secondary coils at least half the axial length of said secondary coils, an armature mounted in said housing, means supporting said armature for reciprocation along the axis of said coils and pins, said armature having a magnetic central portion intermediate said pickup pins whereby reciprocation of said armature varies the reluctance in the magnetic circuit between said armature and said pickup pins, said pickup pins together with a portion of said housing means forming part of the magnetic circuit for the llux from said primary coil whereby the secondary coils are linked through substantially their entire axial length by said ux substantially independently of the position of said armature.

References Cited by the Examiner UNITED STATES PATENTS 2,870,422 1/1959 Gindes et al 336-30 2,923,904 2/1960 Hieber 336-30 2,958,137 11/1960 Mueller 336-30X JOHN F. BURNS, Primary Examiner.

LARAMIE E. ASKIN, Examiner. 

1. IN A TRANSDUCER FOR A GAGE, COMPARATOR OR THE LIKE COMPRISING: MAGNETIC HOUSING MEANS, A PAIR OF COAXIALLY SPACED SECONDARY COILS IN SAID HOUSING MEANS, A PRIMARY COIL IN SAID HOUSING MEANS DISPOSED INTERMEDIATE SAID SECONDARY COILS AND COAXIAL THEREWITH, A MAGNETIC PICKUP PIN FOR EACH OF SAID SECONDARY COILS, SAID PICKUP PINS BEING MOUNTED IN SAID HOUSING TO EXTEND AXIALLY INTO SAID SECONDARY COILS AT LEAST HALF THE AXIAL LENGTH OF SAID SECONDARY COILS, AN ARMATURE MOUNTED IN SAID HOUSING FOR RECIPROCATION ALONG THE AXIS OF SAID COILS, SAID ARMATURE HAVING NON MAGNETIC END PORTIONS DISPOSED AT LEAST PARTLY WITHIN SAID PICKUP PINS AND A MAGNETIC CENTRAL PORTION DISPOSED INTERMEDIATE SAID PICKUP PINS, WHEREBY RECIPRO- 